The tooth is covered with enamel containing hydroxyapatite which is insoluble in the oral environment. Saliva contain abundant minerals close to saturation at normal pH. Fluoride ions in water, from tooth paste, et cetera, can exchange hydroxyl groups in apatite in the teeth. Fluorapatite has lower solubility and it is more acid resistant than hydroxyapatite.
Caries is a disease wherein acid produced by bacteria induce damage by dissolving enamel, dentin, cementum, and potentially bone. These tissues progressively become soft and may eventually break down as ‘holes’. The use of fluorines in fast-setting MTA for caries prevention and treatment has not been described previously.
The minerals in teeth and surrounding fluids are in a back-and-forth exchange. When a neutral pH at the surface of the tooth drops below 5.5, demineralization proceeds faster than remineralization and the mineral structure on the tooth surface can decay and be damaged. Several tooth pastes and also dental materials release fluoride for caries prevention. However, some dental materials are also acidic, which in part may promote demineralization and growth of bacteria.
Glass-ionomer cements with fluoride release have been considered as long-term provisional restorations, however, actually it is not proven by prospective clinical studies whether secondary caries has been significantly reduced by fluoride release from restorative low pH glass ionomer materials (Wiegand et al. 2007). The use of fluorines in fast-setting materials with high pH, such as alkaline MTA for caries prevention has not been described previously.
The ‘nerve’ or the dental pulp is soft tissue with nerves in the center of a tooth. The pulp is surrounded by dental hard tissues. The pulp chamber extends from the crown and down through the root canals. If dental caries or dental traumas are left untreated ‘the nerve’ in the crown and root canals may get infected by bacteria. Such lesions may progrediate and spread through root canals and surrounding bone. Endodontic treatments of pulp and root canals can cure infections or traumas and save the tooth.
Vital pulp tissue can be capped with wound paste if the exposure is clean and small. However, at signs of infection it is often necessary to remove the pulp tissue and clean the pulp chamber and root canals. When this is done, the root canals are sealed and the overlying cavity is filled. Combined prevention and practical treatment of caries and pulp disease by using one fast-setting MTA composition has not been described previously.
The MTA invention introduced by Torabinejad et al. contains Portland cement powder and radiopacitizer particles (US 2005/0263036A1, U.S. Pat. No. 5,415,547). It has primarily been used as an endodontic sealing material in and around teeth. Interestingly, MTA sets in a humid environment, and furthermore it has a high alkalinity which counteracts oral bacteria (U.S. Pat. No. 5,415,547 continued in U.S. Pat. No. 5,769,638). The setting reaction is initiated after mixing powder with water. However, the setting time of MTA is about 3 hours and the material is at risk of being displaced.
The Portland cement powder primarily consist of tricalcium silicate (3CaO.SiO2; C3S), dicalcium silicate (2CaO.SiO2; C2S), tricalcium aluminate (3CaO.Al2O3; C3A) and tetra calcium aluminoferrite (CaO)4.Al2O3.Fe2O3; C4AF). Calcium suphate addition in Portland cement ensures a slow turnover of calcium aluminates. Typically addition of 3-7% of calcium sulphate (gypsum, calcium sulphate dihydrate and/or anhydrite) to portland cement clinker is used for inhibition of calcium aluminate hydration. Test on clinker material for Aalborg White® (C3A<5%) portland cement production ground without gypsum demonstrated long setting times (>1 h). However, this is too long for practical dentistry, such as filling of tooth cavities. It has been unclear which types of cement clinkers ground with or without gypsum that can be used as main component in mineral trioxide aggregate with rapid and controlled setting times typically in the range of 2½-10 minutes.
Addition of calcium chloride to MTA containing Portland cement has been found to accelerate the setting time to 57±3 min (US 2007/0009858 A1). Use of cement-like material with setting times down to 14 minutes was described by (Kao et al. 2009). However, this setting time is relatively long regarding temporary fillings where fast-setting and early strength development is desirable. Typical addition of radiopacitizer to cement or MTA-like material is likely to increase the setting time. Setting times above 10 minutes are, however, impractical regarding e.g. restoration of cavities.
The use of calcium hydroxide is a key treatment modality in operative dentistry and it is used for a wide range of dental applications including caries treatments and endodontics. The use of calcium hydroxide with high solubility as liner, such as in Dycal, at the bottom of deep cavities can, however, lead to wash out of material and loss of overlying filling material (Graiower et al. 1984).
Calcium hydroxide is released from MTA by hydration of calcium oxide (CaO+H2O→Ca2++2OH−), which has favourable bacteriostatic and cariostatic effects The released calcium and hydroxyl ions provide a long-term high pH which is the basis for the important antibacterial effect of using MTA in endodontic treatments. Enterococci resist a relatively high pH of antimicrobial agents. The bacteriocidal effect of calcium hydroxide releasing agents, also on Enterococci, increase with the pH above pH 11. E. faecalis is be about 100-fold more sensitive to killing at pH 12 in comparison to pH 11. Accordingly, the MTA release of calcium hydroxide at high pH is very important.
Addition of calcium aluminates in very high amounts up to 40-60% to Portland cement produce setting times down to 15 minutes (US 2005/0263036 A1) or lower. Extensive replacement of Portland cement, or MTA, with calcium aluminate may decrease the setting time. However, addition of monstrous amount of aluminates at the expense of calcium oxide is a disadvantage. Use of high aluminate containing cement, sulfoaluminate cement, calcium fluoro-aluminate cement, or as reported 40-60% calcium aluminates in MTA (US 2005/0263036 A1) at the expense of calcium oxide, is a major disadvantage especially regarding the favorable effects of calcium hydroxide release on bacteria and caries. Under certain circumstances aluminum in high amount is considered cytotoxic. Apparently, there is a need for MTA for bacteriostatic and cariostatic treatments with fast-setting and significantly lower and moderate calcium aluminate content facilitated by limited gypsum content.
The pulpo-dentinal complex responds to external injuries with dentin sclerosis, dead tracts, and or reparative dentin. Glass ionomer cements (GIC) with fluoride have been used as dental restoration material, isolation cement material below fillings, or e.g. protection of deposited calcium hydroxide before acid etching in order to counteract calcium hydroxide liner wash-out. However, the clinical success by using such materials depends not only on the physical and chemical properties of dental materials, but also on the biological properties (Schmalz and Arenholt-Bindslev 2009).
GIC's with resins typically release chemicals such as HEMA monomer (2-hydroxyethyl methacrylate). Monomers including HEMA and TEGDMA can be eluted and cause genotoxicity and cytotoxicity (Schweikl et al. 2006), and inhibit reactionary dentinogenesis (Goldberg and Smith 2004). Furthermore, HEMA was found to be the most common sensitizer among patients referred for patch testing with acrylate test series. Therefore, the possibility of using more pulp and tissue friendly isolation materials seems relevant.
A material for endodontic treatments with polymers and surfactants, including calcia, silica, and alumina in a so-called ‘dentalcrete’ particulate is described in (WO 2008/08100451). Water-soluble polymers, including PVP, PVA, and hydrolyzed PVA, are used to improve the consistency, similar to using more powder and less liquid, which gives a more putty consistency. Surfactants are added in order to interact with the polymers and improve the fluidity and rheological properties. In a preferred embodiment the C3A content is 5% and the calcium sulphate content is 4%. The use of fluorines, a fast-set favourable aluminate-gypsum ratio, superplasticizer, or other additives, for caries treatment was not described.
Fine particulated MTA with a surface area of up to 1000 m2/kg has been suggested to be able to penetrate thin root canals (US 2005/0263036 A1). However, powder with very large surface area is difficult to hydrate and the powder absorbs increased amounts of water. Ultrafine ground MTA powder requires therefore a significant increase in water-powder ratio to get a manageable consistency. The use of plasticizer in order to decrease the water content was not described.
A material containing a prototype cement blending (Aalborg White®) without gypsum was reported briefly in a study on endodontic material by Camilleri et al. 2005. A non-specific superplasticizer was used for inhibition of flash setting. Details on materials, powder-liquid ratio, setting time et cetera were not reported. Use of fluorine additives, use of material with increased calcium aluminate, use of polyacid-based superplasticizer for reducing the liquid/powder ratio, for prevention and practical treatment of caries were not described.
MTA may contain Portland cement in which low solubility calcium fluoride is added in clinker material before calcination (melting) and grinding of clinkers (US 2005/0263036 A1). Pending US 2005/0263036 A1 suggest that calcium fluoride incorporated in clinker may or may not be released to the surrounding environment. Uncertainty whether calcium fluoride is released from MTA containing calcium fluoride has not been clarified.
Tooth pastes may contain components which enhance remineralization and calm symptoms in sensitive teeth. Studies described fluorine, strontium, and potassium nitrate compounds in tooth pastes may have such symptom calming effect, especially when tiny channels called dentin tubules in the tooth bone (dentin) with nerve endings are open and exposed. A disadvantage when using such materials orally is however a limited symptom calming effect on exposed tubules in a sensitive tooth below a filling.
Zink-Oxygen-Eugenol cement has been shown to decrease symptoms from sensitive teeth. However, placement of eugenol-containing hydrophobic material as intermediary filling prior to the placement of resin restorations may inhibit subsequent polymerization of monomers due to the eugenol, which also may be relatively cytotoxic. Temporary hydrophilic filling material, which both seal, bond, and restore lost dental tissue, prevent caries, decrease symptoms, and furthermore stimulate remineralization and tissue regeneration, has not been described.